Ciaphas Cain seems to get at least one of these per book, despite being... well, himself. The fact that he's bluffing most of the time generally only serves to polish the crown, so to speak.
In the first novel, For The Emperor, he manages to stop a riot involving Guardsmen (and women) from two different factions of an amalgamated regiment by declaring his outrage over the mess they've made and ordering a nearby trooper to go get mops
He gets a minor one in the same novel; after fighting a renegade guardsman in single combat, Amberley shows up with her informal retinue. The guardsman immediately points his hellgun at Cain, threatening to kill him if he makes a move. Cain's response? "Jurgen, kill him."
In The Caves of Ice, the local Adeptus Mechanicus and Administratum senior officials are horrified to learn that their facility is coming under martial law and attempt to bully Colonel Kasteen, the regiment's commander, into repealing the directive. When one of them makes the mistake of saying that she would "prefer the alternative," Cain dramatically drops his laspistol on the table and reveals in no uncertain terms that said alternative is execution for obstruction of the defense of the Imperium. This ends the debate fairly quickly.
Major Broklaw gets one a little bit later on, during another meeting where Ciaphas isn't present.
Colonel Kasteen called the meeting to order. Then she called it to order again. Major Broklaw fired his bolt pistol into the ceiling, and the meeting quickly came to order.
That's not even counting how Cain ends up destroying the Necron army hidden underneath the refinery. he does it by flooding the tunnels with eight million liters of refined promethium and then blowing it all up, producing an explosion so powerful that it buffets the Valhallans' troopship....which is in orbit.
The Ork gargant that's been stomping around through the whole novel also gets a moment when it fights off more than two dozen Necron monolithssinglehandedly. Keep in mind, the gargant is a gigantic, cobbled-together, barely functional walker, taking on a horde of millions-of-years old war machines built by the single most technologically advanced species to have ever existed, and it wins.
An anonymous ork infantryman deserves mention here: stabbed in the chest and left to die by Necron infantry, he proceeds to grab the nearest one, tear its leg off, and beat the thing with it. He dies shortly thereafter, of course, but it was Crazy Awesome while it lasted.
In The Traitor's Hand, a hovercar filled with psychotic, drugged-up Slaaneshi cultists crashes into the top-floor meeting between Commissar Ciaphas Cain and various ultra-high-level officers and governors. Cain wipes the floor with all of the cultists, saving the officers almost single-handedly, and then locates and defuses the bomb hidden in the hovercar. He follows this up with an act absolutely befitting his reputation as a Badass Longcoat when he casually walks over to the drink table for a spot of tea.
The Imperial fleet managed to get one later in the same book. Specifically, a lone cruiser, the flagship Indestructible (commanded by Captain Igor Yates) as well as the thousand-strong merchant fleet it was defending, facing down a Chaos Battleship, and winning, even though none of them had any firepower that could hope to penetrate the battleship's defenses without being obliterated in return. The cruiser, despite being out-gunned, out-ranged and out-classed, defiantly faces down the battleship and exchanges fire with it using its few long-range weapons. The cruiser is apparently crippled by the return volley, and reverses its engines, apparently retreating. The Chaos Battleship, thinking his enemy too badly hurt to fight back, as well as sensing that a Slaaneshi Daemonette had been summoned at the planet, and wishing to end things quickly, moves into short-range to finish the crippled cruiser off. As it looms over the damaged cruiser, the Indestructible quits playing dead and fires a barrage of torpedoes. With that one volley, it cripples the battleship, blowing off most of its primary armament. The ponderous battleship attempts to maneuver for broadside, but fails to notice that in doing so it has lumbered into the center of the merchant fleet, and even if none individually had the strength to hurt it, a thousand tends to add up. When the Indestructible took out its engines, the battleship's fate had been sealed.
Although a single Chaos Marine may not seem like much considering some of the things Cain has fought, the scene from The Traitor's Hand where he went mano a mano with a Khorne Berserker was great. Cain not only survived long enough for Jurgen to blow a hole in its chest with his melta gun, but completely dominated the fight, deflecting the Berserker's attacks with contemptuous ease and taunting it while he did so, making it simply one of the coolest victories he's ever had.
To top it off, he called for a cup of tea even before the corpse was cold. To get an idea of how tough Khorne Berserkers are in the Ciaphas Cain novels, later in the book five of them slaughtered their way through literally hundreds of Slaaneshi cultists.
...until they met the Slaaneshi demon the cultists were summoning, which ripped them apart. Cain and Jurgen then kicked her butt so thoroughly that one of the Tallarn soldiers who witness the battle returns home to found a fringe sect of the Imperial Cult that venerates Cain as a prophet of the Emperor. To quote The Book of Cain, Chapter IV, Verse XXI:
'Then the prophet spake: saying "Frak this, for my faith is a shield proof against your blandishments."'
The real quote was pretty badass too:
"Frak this! My soul's my own and I'm keeping it!"
Cain is consistently described in his novels as one of the best (if not THE best) swordsmen in the whole Galaxy. Which speaks volumes, given that it's 40K, and Cain is basically just a normal man, if large and powerful. And it's not Cain who's saying this about him, either; it's Inquisitor Vail, whose job has likely given her the chance to see plenty of other badasses for comparison.
In Death or Glory, Cain and his band of refugees are trapped in a valley with a massive hydroelectric dam behind them and an approaching Ork warband ahead of them. Cain's solution to this problem is to blow the dam behind them as they fall back and drown the Orks. This may not sound like much of a feat, but consider that the dam had to be blown open with multiple shots from Basilisk artillery and that the warband was a fairly sizeable chunk of the invader's forces (casualties among the orks from this action were estimated at over 7000, while Cain's force was only around 300, including civilians).
Arguably, the entire plot of the novel, in which Cain goes from a survivor of an orbital battle stranded behind Ork lines to the leader of a large force of Imperial irregulars that manages to break the deadlock on the ground by striking the enemy from behind, could count as a single massive Crowning Moment of Awesome. It's no exaggeration to say that Cain's actions literally saved the entire planet in that book, especially given that his adventure culminated in him killing the gigantic ork warboss Korbul in single combat, breaking the back of the waaagh in a single blow (or rather, several rapid pistol shots).
The ending to Duty Calls is a piece of brilliance: After persuading a rogue inquisitor to admit him into his lair, he manages to survive contact with and apparently "purify" a Chaos Artifact of Doom that kills all who touch it. When Inquisitor Vail turns up, the rogue inquisitor discovers the ruse, pulls a gun on Cain and Vail, and flees with the artifact--only to be killed by it while making his escape, as the supposed "purification" was actually due to Jurgen's ability to null psychic power within a small radius.
Making this even more awesome is that, prior to this, Cain spends the entire meeting bluffing his way through on secondhand knowledge and bits and pieces of information he's picked up, knowing full well that the slightest slip-up in talking to these guys about things he doesn't know about will get him killed. Later on, when he's discovered, Cain uses a brilliant combination of his people-reading skills, his own massively fabricated reputation, and his opponents' paranoia to maneuver them into place to bring them both down.
"Flicker", of Amberley's retinue, gets a retroactive Crowning Moment in the same book. His backstory involves bringing down an entire criminal empire, single-handedly, against orders, with just one murder-and-frame.
Earlier in Duty Calls: an airship loaded with promethium and on fire is drifting over the city, built atop a high plateau. Cain improvises a weight (a Chimera APC) to drag the flying bomb away and down. That's excellent quick thinking. Riding along with Jurgen as he drives the Chimera over the cliff, the two of them jumping clear only at the last second -- that's another of the actions that make Cain's repeated claims to be a coward so implausible.
Cain (unwillingly) going toe to toe with a Tyranid hive tyrant, armed with only his chainsword, and defending himself long enough to come out alive. While suffering from a minor but realistic concussion.
Possibly worth noting that most of these are from the same book (The Traitor's Hand).
Praetor (fairly low-level policeman) Kolbe's casual disposal of a Cultist interrupting his vox-conversation with Cain.
'Excuse me a minute...' He was interrupted by a burst of incoherent screaming which sounded like the warcry of a Khornate fanatic and which terminated abruptly in a thud of a power maul on full charge and a gurgle which sounded distinctly unhealthy. 'Well he's not getting mine... Sorry commissar, where were we?'
Cain gets one when he, for once, channels the spirit of a stereotypical Commissar. A Chaos worshipper unleashes sorcery upon him that fills his mind with horrible visions of the destruction of the Imperium and the Emperor himself being devoured by daemons. Through his own will and Jurgen's psychic blank status Cain manages to throw the vision off, roars "Liar!" at the top of his lungs, and blows the psyker's head off, decapitating another with his chainsword.
His true CMOA is posthumous. Thanks to the number of times Cain has been declared MIA or KIA and the amount of time it takes the bureaucracy to sort these out, standing orders were issued to ignore any message declaring him dead. Cain is therefore the only human in the galaxy still listed on the Active Roster despite being buried with full military honours.
Jurgen gets one in The Emperor's Finest. Cain needs Jurgen to shoot out a giant promethium fuel tank a bunch of Orks are using while staying hidden in a space hulk. Jurgen takes three shots before he gets it. Cain is disappointed that there's no visible damage to the tank. The reason? Jurgen was aiming at AND HIT the tank's release valve ... at a distance where Cain didn't think it would be odd to take three shots to hit the tank as a whole.
Cain's plan is to lure the orks out and get them to fight some tyranids for him, and he's briefly worried that Jurgen's attack will end up killing them all before they have a chance to. (It doesn't.)
Cain gets several from the Reclaimers:
Being allowed to use an Astartes training chapel on the basis of his reputation as a One-Man Army.
When he leaves them at the end of his liaison mission, a Space Marine honor guard forms up in the shuttle bay, led by the Brother-Captain commanding this company. Sixty years later, a Reclaimers Brother-Sergeant states that it's "An honour to meet so staunch a friend of our Chapter." This implies the Astartes tell stories about "when Commissar Cain was with us."